Display devices include devices that have displays such as cathode ray tubes (CRTs), liquid crystal displays (LCDs) or other flat panel displays, digital paper, plasma displays, electronic ink displays, or other displays capable of rendering images from electromagnetic input signals. Typically, display devices make use of device-dependent coordinates to define color. For instance, a display device may use red, green, and blue (RGB) coordinates to define color. A CRT display may use different combinations of red, green, and blue phosphors to display colors within the RGB gamut of the display.
Accurate color rendering on a display device is highly desirable. For obvious reasons, it is generally desirable to render visually pleasing images to an end user. However, for some applications, such as “soft-proofing” and other color-intensive imaging applications, very accurate color rendering is imperative.
The term “soft proofing” refers to a proofing process that makes use of a display device rather than a printed hard copy. Traditionally, color proofing techniques have relied on “hard copy proofing,” where proofs are printed out and inspected to ensure that the images and colors on the print media look visually correct. For instance, color characteristics can be adjusted and successive hard copy prints can be examined in a hard proofing process. After determining that a particular proof is acceptable, the color characteristics used to make the acceptable proof can be reused to mass-produce, e.g., on a printing press, large quantities of print media that look visually equivalent to the acceptable proof.
Soft proofing is desirable for many reasons. For instance, soft proofing can eliminate the need to print hard copies on media during the proofing process. Moreover, soft proofing may allow multiple proofing specialists to proof color images from remote locations simply by looking at display devices. Soft proofing can be faster and more convenient than hard proofing. Moreover, soft proofing can reduce the cost of the proofing process. For these and other reasons, soft proofing is highly desirable.
Realizing soft proofing, however, has proven to be very difficult. For instance, the inability to achieve adequate color matches between hard copies and images presented on display devices has generally limited the effectiveness of soft proofing.
Color management tools and techniques have been developed to improve the accuracy of color matching between the outputs of different devices. For instance, color profiles used to categorize and define imaging devices, and color matching software such as color matching modules (CMMs) have been developed for this purpose.
Color profiles, for instance, can be used to categorize and define a device that was used to image a particular color image. A color profile is a data structure that describes the color characteristics of a particular device. A color profile may include color information such as information describing how the device converts from device-independent coordinates to device-dependent coordinates and vice versa. In some formats, color profiles may include information categorizing the print media used (in the case of a printer) or information categorizing the phosphors (in the case of a CRT display).
Color matching modules (CMMs) are computer programs that facilitate accurate color matching. A CMM may implement an algorithm or a look-up table, for instance, to match the color output between two different devices. Using respective color profiles as input, a CMM may alter the colorimetric characteristics of color data that is sent to a second device so that the output of the second device will be a more accurate visual match to that of the first device.
A CMM is loaded on a computer that controls the second device. The second device may automatically provide the CMM with its color profile. When an image is sent to the second device, for instance, an additional file may be appended to the image to provide the CMM with the color profile of the first device. In this manner the CMM may obtain the input necessary to perform a color matching algorithm. Thus, the input to the second device can be adjusted so that the output of the second device more accurately matches the output of the first device.
In this document the term image refers broadly to any type of graphical rendering. For example, an image could simply be a page of text, a picture, a chart, or another pictorial device such as user interface elements like buttons or windows generated by a computer's operating system software. Generally, a graphical element or any collection of graphical elements can comprise an image.